The Key to iMessage Harmony Across Devices
With the recent release of the beta of the “Messages” app that will be shipping with OS X Mountain Lion, we’re one step closer to unified messaging bliss. However, there is a simple trick to getting everything working across devices. The key is to make your “Caller ID” the same everywhere you use iMessage. With the Mac app, change your setting in the specified place from the “Preferences” menu. For iOS, you can find it in: Settings -> Messages -> Receive At -> Caller ID. I’d recommend setting it to your primary email address (it doesn’t need to be your Apple ID).
Once this is done, no matter which compatible device you’re messaging from, it will show up to people as the same Caller ID. So as long as you register the Caller ID email address on each device, your iMessages will seemless go to every device in your aresenal.